New research leads to stretchable 3D prints that test structural strength

Dec 25, 2014 | By Simon

While we've previously seen materials change color digitally through the use of analysis tools in 3D modeling programs, we soon may be able to test structural strength in their physical form through the use functional 3D printing polymers.

Led by Researchers from the University of Washington, the new research is focused on using 3D printing as a way of approaching the fabrication of easy-to-read mechanical force sensors, which would be nearly impossible to fabricate using standard manufacturing methods.

Sensor-based polymers, which are able to change shape or composition in response to light, temperature and force, have proven to be a challenge to work with when designing products such as drug delivery devices. Primarily, the sensitive reactive properties of the materials become prematurely activated through traditional manufacturing methods that require high-heat and other disruptive factors in the process of creating the final product.

Functional polymers change shape or composition in response to stimuli such as light, heat, and mechanical force, and hold promise as sensors or in drug delivery devices.
Credit: ACS Appl. Mater. Interfaces

Researchers have found a way to counteract this by using molds when working with the material, however the natural limitations of working with molds has limited the shape and complexities of the final design direction.

Led by Assistant Professor of Chemistry Andrew J. Boydston, the University of Washington team has been focusing the majority of their efforts on using commercial 3D printers with these sensitive materials to create force sensors that change color when stretched.

In their initial development efforts, the researchers first developed a mechanosensitive polymer that could withstand being extruded by a commercial 3D printer without changing color or being damaged by heat.

The team then focused on testing the material by creating a dog bone-shaped device (wide on the sides, narrow in the middle) made of commercial polycaprolactone with an inner stip of spiropyran-containing polymer.

Spiropyran units in a polymer (left) isomerize into a purple merocyanine (right) when the material is stretched. Credit: ACS Appl. Mater. Interfaces

When pressure is applied to either end of the device, the newly-deformed shape turns purple based on the reactive forces to the spiropyran-containing polymer strips. Applications for their discovery could include measuring the structural load of a particular material or to track the amount of times a material experience a particular force.

In order to test their findings, the researchers created another 3D print using the same material and embedded four squares of the color-changing spiropyran polymer inside. By applying varying degrees of force to the entire structure, they were able to further test the accuracy by counting the resulting embedded purple squares.

According to Boydston, creating a device with one material embedded into another... especially sensitive sensor-based material...is relatively difficult to prepare with molds, however 3D printers are able to create the devices quickly and easily.

Whether the end user is a researcher who needs to quickly reproduce devices with mechanically sensitive polymers or if an engineer needs to test the structural strength of a prototype, the research findings are without a doubt an exciting development for those who rely on rapid prototyping for aiding in their design and development process.